With the evolution of technology, mobile electronic devices, such as smart phones and tablet PCs, play essential roles gradually in daily lives. For the current design trend, the mobile electronic devices like smart phones or tablet PCs usually set touch screens in order to let users operate intuitively. Only about one to three physical buttons are set and remained on the mobile electronic devices to provide controlling settings, such as booting the electronic devices or volume, for users. Nevertheless, when the mobile electronic devices are manufactured, the corresponding functions of these physical buttons have been usually preset by their manufacturers, and in general, users are incapable of randomly defining the corresponding functions of these buttons.